Power backplane with distributed hotspot detection grid

ABSTRACT

Systems and methods are provided for providing thermal protection to a power backplane printed circuit board. A distributed hotspot detection grid is included in the printed circuit board, the distributed hotspot detection grid comprising a plurality of passive temperature sensors spread across the printed circuit board to measure temperature increases. The plurality of passive temperature sensors are connected to a detection circuit for comparing signals from the passive temperature sensors to a reference signal. If the temperature increases on the PCB, electrical characteristics of at least one passive temperature sensor will change, resulting in a change of the input signal to the detection circuit. When the threshold is exceeded (indicating a potential short circuit or hotspot), the detection circuit outputs a shut down signal to the one or more power supplies connected to the of the backplane printed circuit board, to avoid catastrophic damage to the printed circuit board.

BACKGROUND

Power is distributed within servers generally through the use of a powerbackplane. A conventional power backplane typically includes a printedcircuit assembly (PCA) generally consisting of a printed circuit board(PCB) with electrical traces connecting one or more power supplies to anumber of components and other loads requiring power. The powerbackplane typically also includes electrical connectors to interfacepower from one or more power supplies to the units connected to thebackplane. In some applications, power interface boards may be includedto allow interfaces to pluggable power supplies, headers, utilityconnectors and so on.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure, in accordance with one or more variousembodiments, is described in detail with reference to the followingfigures. The figures are provided for purposes of illustration only andmerely depict typical or example embodiments.

FIG. 1 illustrates an example power system with power supplies and a PCBincluding a distributed hotspot detection circuit in accordance withembodiments of the technology disclosed herein.

FIG. 2 illustrates an example distributed hotspot detection grid inaccordance with embodiments of the technology disclosed herein.

FIG. 3 illustrates another example distributed hotspot detection grid inaccordance with embodiments of the technology disclosed herein.

FIG. 4 illustrates an example method for providing power system hotspotprotection in a server in accordance with embodiments of the technologydisclosed herein.

FIG. 5 illustrates an example method for operating a power system with adistributed hotspot detection grid in accordance with embodiments of thetechnology disclosed herein.

The figures are not exhaustive and do not limit the present disclosureto the precise form disclosed.

DETAILED DESCRIPTION

As processing speeds and complexity increase, servers are increasinglydrawing more and more power. This increase has corresponded with a focuson increasing the density within servers, including more and morecomponents and sub-assemblies within a smaller area. Multi-layered PCBshave helped to facilitate higher component density and design complexityby enabling a greater number of electrical traces to be available foruse in distributing power to components. As the voltage to the servertends to remain constant, these two trends have led to more powerneeding to be dispersed over a smaller area, thereby resulting in higherand higher current levels within the power backplane.

The increased current levels within a smaller area raises the potentialfor catastrophic failure of the power backplane. Due to the increasingdensity, the spacing between conductive layers in the PCB of the powerbackplane has continued to decrease. This small separation requiresnear-perfect precision in manufacturing the power backplane to avoidphysical defects in the PCB that may create short circuits. Moreover,the increased heat caused by the increased power being dissipatedthrough the power backplane raises the potential impacts ofelectromigration (embodiments of the phenomenon in the PCB field knownas copper migration). Slight discrepancies in the spacing between layersadds to the potential for copper migration to occur at a more rapid ratethan anticipated, resulting in the board failure earlier than itsexpected life span.

With the increased current levels within the system, the potential forshort circuits to develop on the power backplane, resulting in“hotspots,” also increases. Although power supplies may have overcurrentprotection (forcing a shut down when the current being pulled by theloads exceeds the power supplies' rating), the high-power requirementsin high-density server designs makes it possible that a short circuit onthe PCB of the power backplane may not trigger the overcurrentprotection. For example, if there are 1000 amps of power available fromthe power supplies, the power supplies can feed a short circuit that isonly pulling 600 amps without tripping the power supplies' overcurrentcircuitry. In this example, that 600 amps would continue to go throughthe hotspot, generating a large amount of heat, potentially melting theboard, causing damage and delamination.

Generally, these hotspots are relatively small compared to the size ofthe PCB of the power backplane (e.g., the PCB may be 18″×24″, and thehotspot may be 0.5″×0.5″), making it difficult to effectively monitorand identify hotspots before damage occurs. Some servers may includeactive temperature sensing devices. Active temperature sensing devices(interchangeably, active temperature sensors) are generally externaldevices designed to monitor a component within a system, whetherdirectly connected to the component or through some transmission medium.Active temperature sensing devices require their own power source and,traditionally, require a processing device to read signals and make adecision based on the readings. The active temperature sensors used inservers today tend to be designed to monitor the temperature ofcomponents that are known to get hot, such as ASICs, processors, harddrives, etc. The predictability with which such components may generateheat makes it easier to design an active temperature sensing device foreffectively monitoring the components. For example, it is possible toidentify specific areas of the components that may generate heat atdangerous levels during a problem situation. Or, as another example, thecomponent itself may be expected to generate heat uniformly, allowingfor a broad scope active temperature sensor to be designed to monitorwhether the generated heat reaches a dangerous level.

However, the predictability of heat generation when a short circuitoccurs on a PCB is much lower. First, manufacturers do not anticipatedangerous heat generation to occur in a properly manufactured PCB, solittle to no attention is paid to how best to measure heat generation.Second, unlike the other components of a system discussed above, it isnear impossible to know where a short circuit may appear on a PCB. Whenthe short circuit is caused by damage during manufacture orinstallation, it is highly improbable that one can predict exactly wherea short circuit may develop, acutely where the PCB comprises multiplelayers (many not visible). Third, as discussed above, a hotspot could beminiscule relative to the size of the board. Therefore, designing anactive temperature sensor that can effectively sense heat indicative ofa potential hotspot before the heat reaches a dangerous level is highlycomplex and improbable. The sensitivity that would be required of anactive temperature sensor to sense a small hotspot on the PCB boardthrough a transmission medium (e.g., air) would not be functional withinthe system environment, where there are plenty of components thatgenerate a certain amount of heat inherently. Moreover, because of thesize and requirements of the components of an active temperature sensor,blanketing the PCB with a sufficient number of active temperaturesensors would be impractical, as there would not be sufficient spacewithin the already dense system enclosure.

Further, the potential damage caused by an undetected hotspot to the PCBitself could render the use of active temperature sensing devicesineffective. Active temperature sensing devices connected to the PCB anddesigned to detect a temperature value usually require a connection to aprocessor. The processor reads the data from the active temperaturesensing device to determine whether the temperature is at or exceeding acertain threshold and to send an emergency shutoff signal to the powersupplies if necessary. However, if the active temperature sensing devicecannot effectively sense the entire area of the PCB, it may not be ableto detect a hotspot before damage occurs. For example, the hotspot maybe just outside the sensing area of the active temperature sensingdevice, and only after the heat has dispersed further from the actualhotspot would it be detected. At this point, the board may have alreadybeen damaged. This damage could impact the circuit connecting the activetemperature sensing device to the processor, reducing the reliability orcompletely cutting off the sensing capability. The damage could alsoimpact the connection between the processor and the power supplies,making it impossible for the processor to send the emergency shutoffsignal to the processors, exacerbating the situation.

Embodiments of the present disclosure may be implemented to preventcatastrophic damage to the power backplane through effective detectionof areas on the board that are getting too hot prior to damageoccurring. A grid of passive temperature sensors are distributed acrossthe PCB, providing a distributed hotspot detection circuit. Passivetemperature sensors are generally electrical components whose electricalcharacteristics are reactive to temperature changes surrounding thecomponent. Such components do not require an external power source foroperation (e.g., can use the same control voltage Vcc of othercomponents of a PCB), are small (usually having the form factor of a PCBcomponent, like a resistor or a capacitor), and can be included directlyon the PCB. In various embodiments, the passive temperature sensors mayinclude negative temperature coefficient (NTC) thermistors, resistancetemperature detectors (RTDs), positive temperature coefficient (PTD)thermistors, thermocouples, or other passive temperature sensors. Bydistributing a plurality of such passive temperature sensors, potentialshort circuits or hotspots may be detected before there is sufficientheat to cause damage to the PCB. Unlike active temperature sensors,passive temperature sensors do not require an external power source tooperate, do not need to interface with a processor or microprocessor,and are less expensive. In various embodiments, the distributed hotspotdetection grid includes a detection circuit connected to the pluralityof passive temperature sensors. When a connected passive temperaturesensor registers a temperature rise, its output voltage will change.This will result in the output of the detection circuit switching fromone state to another, signaling the power supplies connected to the PCBto turn off.

FIG. 1 illustrates an example power system 100 with power supplies and aPCB including a distributed hotspot detection circuit in accordance withembodiments of the technology disclosed herein. For ease of discussion,the electrical traces between the components of the power backplane 100have been omitted, but a person of ordinary skill in the art wouldunderstand how to design the electrical traces required in light of thepresent disclosure.

As illustrated, this example power system 100 includes a PCB 104 thatinterfaces to one or more power supplies 102 a, 102 b, 102 c, 102 d.Power from the power supplies 102 a, 102 b, 102 c, 102 d is disseminatedvia traces of PCB 104 to sub-assemblies and other component loads (notpictured) that may be connected to PCB 104. In various embodiments, thePCB 104 includes one or more interfaces to connect with each of thepower supplies 102 a, 102 b, 102 c, 102 d. In some embodiments,removable connectors may be used such that one or more of the powersupplies may be swapped out as needed. In other embodiments, one or moreof the power supplies 102 a, 102 b, 102 c, 102 d may be hardwired to PCB104 The PCB 104 also comprises a number of connectors for varioussub-assemblies and components of a server. Electrical traces on the PCB104 enable the components to draw power from, and thereby place a loadon, the one or more power supplies.

The power PCB 104 also includes a distributed hotspot detection circuit106 (interchangeably referred to as “a distributed hotspot detectiongrid” in the present disclosure). The distributed hotspot detectioncircuit 106 may include a plurality of passive temperature sensors 108dispersed across the PCB 104, and a detection circuit 110 to detect overtemperature conditions based on a voltage (or in some embodiments acurrent) presented to the detection circuit 110 by passive temperaturesensors 108.

In various embodiments, the quantity of passive temperature sensors 108included may vary depending on factors such as, for example, thesensitivity of the passive temperature sensors 108 to changes intemperature, and the resolution with which over-temperature conditionsare desired to be detected. For example, for PCBs with a denser routingof traces, it may be desirable to place passive temperature sensors 108more closely together to better identify the specific traces that may becausing the over-temperature condition. Less dense routing on the PCBmay allow greater spacing (or density) of temperature sensors 108 whilestill achieving the ability to identify the traces responsible for theover-temperature condition. Device sensitivity may also play a role indetermining the density with which temperature sensors 108 arepositioned on PCB 104. Devices with greater sensitivity may be able toreact to over-temperature conditions at a distance farther away from thedevice then when those devices with lesser sensitivity. However, using amore sensitive device to cover a larger area may result in a sacrificeof resolution and therefore the inability to pinpoint the specifictraces responsible for an over-temperature condition.

In some embodiments, passive temperature sensors 108 may be implementedusing negative temperature coefficient or NTC thermistors. An NTCthermistor is a resister whose resistance has an inverse relationship toheat; as the temperature increases, resistance decreases. Thesensitivity of the NTC thermistor can be large, enabling large changesin resistance in response to small changes in temperature. The higherthe resistance of an NTC thermistor, the larger the temperaturecoefficient. Other devices can be used as passive temperature sensors108 in various embodiments to signal an increase in temperature such as,for example, resistance temperature detectors (RTDs), positivetemperature coefficient (PTD) thermistors, thermocouples, or otherpassive temperature sensing devices. In various embodiments, thedistributed hotspot detection circuit 106 may include one or moredifferent types of passive temperature sensors.

In various embodiments, the number of passive temperature sensors 108and their arrangement may be determined based on characteristics of thePCB 104. Non-limiting examples of characteristics of PCB 104 that mayimpact the number and arrangement of passive temperature sensors 108include: number of conductive layers of the PCB 104; thickness of eachconductive layer; spacing of dielectric or non-conductive layers betweenthe conductive layers; surface area of the PCB 104 exposed to air;potential airflow across the PCB 104; density of components andsub-assemblies on the PCB 104; number of vias used to interconnectbetween layers; among other characteristics of the PCB 104. Based on thecharacteristics, a designer may determine an expected temperature dropoff within a PCB 104 and determine the number and arrangement of passivetemperature sensors 108 which would allow the distributed hotspotdetection circuit 106 to cover the PCB 104 near completely. For example,based on a certain set of data, a designer may determine that thetemperature drops off by 2° per inch as you move away from a hotspot,and that this can equate to a grid capable of sensing any hotspottemperature within ˜5° with passive temperature sensors 108 with 4″spacing. Using this spacing, the designer can determine the number ofpassive temperature sensors 108 required.

As noted above, the power system 100 further includes a detectioncircuit 110 that can be used to detect an increase in temperature or anover-temperature condition using voltage or current levels provided todetection circuit 110 by temperature sensors 108. In some embodiments,detection circuit 110 may comprise a plurality of comparatorselectrically connected to passive temperature sensors 108, and connectedto switch off an offending power supply when the voltage level providedby a connected passive temperature sensor 108 exceeds a thresholdvoltage. In various embodiments, where more than one type of passivetemperature sensor 108 is included, each type of passive temperaturesensor 108 may be connected to its own detection circuit 110. In suchcases, multiple detection circuits 110 can be disposed on the PCB. Invarious embodiments, where more than one type of passive temperaturesensor 108 is included, each type of passive temperature sensor 108 maybe connected to a specific section of the same detection circuit 110.

As a more specific example, a plurality of NTC thermistors areimplemented as passive temperature sensors 108 are connected with thedetection circuit 110, comprising a plurality of comparators, throughelectrical traces on the PCB 104. A comparator circuit is a circuitdesigned to compare two signals and to output a signal based on thecomparison. In various embodiments, the comparator circuits of detectioncircuit 110 can compare the voltage level from a passive temperaturesensor 108 against a reference voltage. Each comparator circuit has athreshold voltage change which, when exceeded, causes the output of thecomparator circuit to change (e.g., from HIGH to LOW, or from LOW toHIGH). The passive temperature sensors 108 and the detection circuit 110may be tuned so that the detected temperature that will cause thedetection hotspot detection circuit 106 to trip is higher than adesignated high-end of a nominal operating temperature range (or in someimplementations higher than the worst case operating temperature) of thepower system 100, but lower than the temperature where damage may occurto the PCB 104, such as delamination, melting, etc.

In various embodiments, the detection circuit 110 may comprise aplurality of comparator circuits equal to the number of passivetemperature sensors 108 within the distributed hotspot detection circuit106. In such embodiments, each passive temperature sensor 108 would haveits own corresponding comparator circuit (i.e., a 1-to-1 relationship).In other embodiments, one or more passive temperature sensors 108 may beconnected in parallel to the same comparator circuit within thedetection circuit 110. For example, a multiplexer or other like circuitcan be used to accept multiple inputs from a plurality of passivetemperature sensors 108 and provide them one at a time or simultaneouslyto the input of the corresponding comparator circuit. For example, invarious embodiments the plurality of passive temperature sensors 108 maybe partitioned into a plurality of subsets, each subset comprising oneor more passive temperature sensors 108. Each subset can be associatedwith a different comparator circuit, with the passive temperaturesensors 108 of each subset being connected to its associated comparatorcircuit in parallel. As each subset is associated with a differentcomparator circuit, each passive temperature sensor 108 is monitored byonly one comparator circuit.

Where multiple comparator circuits are included within the detectioncircuit 110, the output of each comparator circuit is connected to theoutput of the detection circuit 110. Therefore, if any comparatorcircuit within the detection circuit 110 detects an overtemperaturecondition, the corresponding power supplies can be shut down. In stillother embodiments, the detection circuit 110 may be a single comparatorcircuit to which all of the passive temperature sensors 108 areconnected.

In various embodiments, the output signal of the detection circuit 110may be connected to a “kill” switch of each of the power supplies 102 a,102 b, 102 c, 102 d. For example, the output signal of the detectioncircuit 110 may be connected to an overcurrent protection circuit ofeach power supply 102 a, 102 b, 102 c, 102 d such that, when the outputsignal of the comparator component changes state, it triggers theovercurrent protection circuit of all the power supplies, or of theaffected one or more power supplies. In other embodiments, the killswitch may be a latching device within the power supply 102 a, 102 b,102 c, 102 d, such as a silicon-controlled rectifier (SCR) device, thatis triggered by the change in output from the detection circuit 110. Insuch cases, the power supplies 102 a, 102 b, 102 c, 102 d will not beable to restart following a detected temperature event by thedistributed hotspot detection grid 106 until the units are disconnectedfrom input power (e.g., the input cable to the power supplies isdisconnected). In various embodiments, the kill switch device may beincluded on the PCB 104, configured to shut down each of the powersupplies 102 a, 102 b, 102 c, 102 d, while in other embodiments theremay be multiple kill switch devices configured to send the shut downsignal to one or more of the power supplies 102, 102 b, 102 c, 102 d. Inother embodiments, the kill switch device may be built into the powersupplies 102 a, 102 b, 102 c, 102 d, and the detection circuit 110 maybe connected to an interface of the power supplies to the kill switchdevice.

In various embodiments, the kill switch device used to shut down thepower supplies 102 a, 102 b, 102 c, 102 d may be designed such that abaseline output of the detection circuit 110 is required to be sensed,otherwise the kill switch device will trigger. In this way, thedistributed hotspot detection grid 106 can provide protection in theevent the PCB 104 is damaged prior to detection by one or more of thetemperature sensors 108. When damage to the board disrupts theconnection between any of the NTC thermistors and the detection circuit110, or between the detection circuit 110 and the kill switch device,the signal will change from the baseline, triggering the kill switchdevice to signal a shut down. In this way, the distributed hotspotdetection grid 106 may minimize the damage sustained to the power system100.

The output of the detection circuit 110 may be designed in someembodiments to not allow the power supplies 102 a, 102 b, 102 c, 102 dto power up in a first instance. The baseline signal of the detectioncircuit 110 (i.e., the state of the detection circuit 110 during normaloperation) may be designed to be equal to the signal needed by the powersupplies 102 a, 102 b, 102 c, 102 d to turn on. The detection circuit110 output can be tied in with other operational signals necessary forthe power supplies 102 a, 102 b, 102 c, 102 d to power on in the firstinstance. Power supplies generally include an auxiliary voltage output(separate from the main power output) that powers one or moreoperational signals necessary to turn on the main power output. Invarious embodiments, the operational signals may include an enablesignal used to turn on the power supply and an internal “kill” signalfor immediately shutting down the power supply. In some embodiments, theenable signal may be the signal indicating that the power supply hasbeen properly connected. In some embodiments, the output of thedetection circuit 110 may be tied into one or both of these signals. Forexample, in some embodiments, the output of the detection circuit 110may be tied to the basic “kill” signal that is included within powersupplies 102 a, 102 b, 102 c, 102 d. Unless the baseline output signalof the detection circuit 110 is present when the power supplies areconnected, none will be able to power on. The signal may not be presentat baseline due to damage already sustained by the PCB 104 or because ofa fault within the distributed hotspot detection grid 106. By tying theoutput to the operational signal circuit of the power supplies, thepower supplies will not turn on absent the baseline output of thecomparator circuit. In this way, if the board does sustain damage andthe connection between the distributed hotspot detection circuit and thepower supplies is impacted, the power supplies will not turn on.

As illustrated in FIG. 1, in various embodiments the detection circuit110 is disposed on the opposite end of the PCB 104 from the powersupplies 102 a, 102 b, 102 c, 102 d. Having the detection circuit 110located on the far end from the power supplies enables the distributedhotspot detection grid 106 to monitor the entire PCB 104 for hotspots.Extending the distance between the detection circuit 110 and the powersupplies also increases the distance the output of the comparatorcircuit 110 has to travel across the PCB 104, helping to identify if theboard is already damaged, as discussed above.

FIG. 2 shows an example distributed hotspot detection grid 106A inaccordance with embodiments of the present disclosure. For ease ofdiscussion, the illustration includes only some of the circuit elementsthat would be included in operation. For example, ground and controlsignals have been omitted, as well as any noise suppression circuitry(e.g., capacitors) that could be included in various embodiments of thetechnology. A person of ordinary skill in the art would know how toconnect grounds and implement routinely used noise suppressioncomponents.

Referring to FIG. 2, the distributed hotspot detection grid 106Aincludes three passive temperature sensors 108 a, 108 b, 108 c. Thesymbol used for passive temperature sensors 108 a, 108 b, 108 c in FIG.2 (and in FIG. 3) is that of an NTC thermistor. Although the illustratedexample(s) uses NTC thermistors, various embodiments can use anotherpassive temperature sensor, such as those discussed above with respectto FIG. 1. For purposes of discussing FIGS. 2 and 3, the passivetemperature sensors 108 a, 108 b, 108 c, 108 d, 108 e, 108 f can bereferred to interchangeably as “NTC thermistor(s).” The number ofpassive temperature sensors 108 a, 108 b, 108 c has been limited forease of discussion and the number of passive temperature sensors 108 a,108 b, 108 c illustrated in FIG. 2 should not be interpreted as limitingthe scope of the technology. In various embodiments, a differentquantity of passive temperature sensors 102 a, 102 b, 102 c can beincluded within the distributed hotspot detection grid 106A, dependingon the size of the PCB, the resolution desired, the sensitivity ofpassive temperature sensors 108 a, 108 b, 108 c, and so on.

In this example, each NTC thermistor 108 a, 108 b, 108 c is connected toa corresponding comparator circuit 204 a, 204 b, 204 c. As illustrated,a detection circuit 110 a comprises three comparator circuits 204 a, 204b, 204 c. The voltage level from the NTC thermistors 108 a, 108 b, 108 cserves as an input to the comparator circuit 204 a, 204 b, 204 c ofdetection circuit 110 a, respectively. The detection circuit 110 acompares the voltage levels from the NTC thermistors 108 a, 108 b, 108 cagainst a reference voltage Vref supplied by a power supply. The Vrefserves as a threshold voltage against which the voltages from NTCthermistors 108 a, 108 b, 108 c are compared for triggering a change inthe output of the comparator circuit 204 a, 204 b, 204 c. When thevoltage level from one of the NTC thermistors 108 a, 108 b, 108 cincreases (due to the resistance of the NTC thermistor dropping due to atemperature increase) to a voltage level above Vref, its correspondingcomparator circuit 204 a, 204 b, 204 c switches its output signal to adifferent state (e.g., from a LOW to HIGH state or vice versa). Vref canthus be selected as a voltage level equal to the voltage that would beoutput by NTC thermistors 108 a, 108 b, 108 c should their temperaturereach the minimum over-temperature condition to be tolerated by thesystem design.

The outputs of the comparator circuits 204 a, 204 b, 204 c are connectedto a detection circuit output 210. In the illustrated example, a singleoutput 210 is used to signal an over-temperature condition. The signalcan be set to generate an alert as to the over-temperature condition andto shut down the power supplies to prevent further damage. The detectioncircuit output 210 may be connected to the power supplies of the powersystem, like power supplies 102 a, 102 b, 102 c, 102 d discussed withrespect to FIG. 1, to send a signal causing the power supplies to shutdown. Where all of the comparator circuits are tied to a single output,all of the power supplies can be shut down based on an over-temperaturecondition being sensed by a single thermistor. In some embodiments,where the comparator circuits are tied to a single output, an indicatorcomponent may be included in each comparator circuits 204 a, 204 b, 204c. The indicator component can be used to identify which of thecomparator circuits 204 a, 204 b, 204 c triggered the shutdown signal tobe sent to the power supplies. In this way, the location of thetemperature increase within the PCB 104 may be more easily pinpointed byidentifying the passive temperature sensor 108 a, 108 b, 108 c tied tothe triggered comparator circuit. In various embodiments, the indicatorcomponent may be a latch. In other embodiments, the indicator componentcan be a fuse tied to the output of the comparator circuit, designed totrip on an over-temperature condition (i.e., trip at the voltage leveloutput when such a condition is detected). Diodes 206 a, 206 b, 206 cmay be included in the comparator circuits 204 a, 204 b, 204 c to ensurethat current on the detect circuit output 210 does not flow into thecomparator circuits 204 a, 204 b, 204 c.

In some implementations, each of the comparator circuits 204 a, 204 b,204 c can have its own output connected to shut down a specific one ormore of the plurality of power supplies in the power system. Forexample, a given comparator circuit output can be coupled to the powersupply or power supplies that provides power to the traces within thesensing range of the thermistor corresponding to that given comparatorcircuit. Accordingly, only the power supply or supplies corresponding tothe offending short circuit need to be shut down to alleviate theover-temperature condition.

FIG. 3 illustrates another example distributed hotspot detection grid106B in accordance with embodiments of the present disclosure. Asillustrated, multiple NTC thermistors 108 d, 108 e, 108 f are connectedin parallel to the same comparator circuit 204 in the detect circuit 110b. In various embodiments, the plurality of NTC thermistors (asdiscussed with respect to FIG. 1) may all be connected in parallel asillustrated to a single comparator circuit 204. In other embodiments,multiple comparator circuits 204 may be included in the detectioncircuit 110 b, each connected to one or more NTC thermistors connectedin parallel. NTC thermistors are used simply as an example; any of thepassive temperature sensors discussed with respect to FIG. 1 may be usedin a similar manner.

Using a distributed hotspot detection grid 106 as described with respectto FIGS. 1-3 enables effective monitoring for short circuit andtemperature issues associated with a power system without impacting theoverall design of the system. The grid can be included on a PCB of thepower system without increasing the overall footprint, and withoutunduly impacting the density of the system. The embodiments discussedenable for effective local temperature monitoring of the PCB that is notpossible with current active thermal sensing devices in servers. Thesmall size and minimal intrusion of passive temperature sensors (e.g.,NTC thermistors) address the unpredictability of thermal issues on thePCB in an effective, reliable, and low cost manner.

FIG. 4 illustrates an example method 400 for providing power systemhotspot protection in a server in accordance with embodiments of thetechnology disclosed herein. At operation 402, a distributed hotspotdetection grid is distributed on a PCB. The distributed hotspotdetection grid may be similar to the distributed hotspot detection grid106 discussed with respect to FIGS. 1-3, and the discussion above isapplicable here. In various embodiments, the distributed hotspotdetection grid comprises a plurality of passive temperature sensors anda detection grid. Non-limiting examples of passive temperature sensorsinclude: negative temperature coefficient (NTC) thermistors; resistancetemperature detectors (RTDs); positive temperature coefficient (PTD)thermistors; or thermocouples; among other passive temperature sensors.

At 404, an increase in temperature somewhere on a PCB board is sensed byat least one passive temperature sensor distributed on the PCB. When anincrease in temperature is sensed, one or more electrical properties ofa least one passive temperature sensor distributed on the PCB changes,causing a change in the voltage level across the passive temperaturesensor. Accordingly, the voltage level on the output of the passivetemperature sensor changes.

At 406, the voltage level on the output of the at least temperaturesensor is received by a detection circuit. In various embodiments, thedetection circuit is similar to the detection circuit 110 discussed withrespect to FIGS. 1-3. The detection circuit is connected with the outputof the plurality of passive temperature sensors, such that the output ofthe at least one passive temperature sensor serves as an input to acomparator circuit of the detection circuit.

At 408, the detection circuit detects the increase in temperature on thePCB. A comparator circuit of the detection circuit, connected to thepassive temperature sensor by an electrical trace on the PCB, registersthe change in the voltage level and compares it against a thresholdvalue. In various embodiments, the threshold value may be a referencevoltage Vref. If it does not exceed a threshold value, the comparatorcircuit does not change. If the voltage level does exceed the thresholdvalue, the comparator circuit changes its state (similar to the changediscussed with respect to FIGS. 2-3), and the change in state makes thedetection circuit output a shut down signal to one or more powersupplies of the power system at operation 410. In various embodiments,the signal from the detection circuit may trigger a latching devicelocated within the power supplies, while in other embodiments thelatching device may be on the PCB of the power system.

FIG. 5 illustrates an example method 500 for operating a power systemwith a distributed hotspot detection grid in accordance with embodimentsof the present disclosure. At operation 502, the power supply checkswhether it has received one or more control signals necessary to poweron. In various embodiments, the necessary control signals may includethe operational signals of the power supply discussed above with respectto FIGS. 1-4, such as the enable signal. In various embodiments, thebaseline output signal from the distributed hotspot detection grid maybe included as a necessary signal for the power supplies to power on, asdiscussed with respect to FIG. 1. If all signals have not been received,at operation 504, the power supplies remain in a power-off state. Invarious embodiments, the signal from the distributed hotspot detectiongrid may not be received due to damage to the PCB that occurred earlier,either during manufacture of the PCB itself or the power systemassembly. If all signal have been received, the power supplies willpower on at operation 506 and begin to provide power to the power systemfor distribution to sub-assemblies and other server components.

At operation 506, one or more of the power supplies detect a change inthe output signal from the distributed hotspot detection grid. Thedistributed hotspot detection grid may be similar to the distributedhotspot detection grid discussed with respect to FIGS. 1-3. In variousembodiments, the change in the output signal may be based on a change inthe electrical properties of at least one passive temperature sensor.For example, where the passive temperature sensors of the distributedhotspot detection grid include one or more NTC thermistors, the changein output signal may indicate that one or more of the NTC thermistorsdetected a temperature increase indicative of a short circuit orhotspot. In other embodiments, the change in the output signal may occurdue to undetected damage that occurred which has impacted or severed theconnection between the distributed hotspot detection grid and the one ormore power supplies. Either way, the change in signal is recognized as ashut down signal by the one or more power supplies. In response to thechange in the output signal of the distributed hotspot detection grid,the power supplies shut down at operation 510. In some embodiments, thechange in output signal may be detected by an overcurrent protectiondevice of the power supply to which the output signal from thedistributed hotspot detection grid is connected. In various embodiments,the change in output signal may be detected by an SRC device in thepower supply to which the output signal from the distributed hotspotdetection grid is connected. In some embodiments, a latching device maybe included in the power supplies, and the one or more power suppliesmay latch in the power-off state at operation 512. The power supplieswould stay powered-off in such embodiments until being disconnected fromthe external power source, thereby resetting the latching device.

In common usage, the term “or” can have an inclusive sense or exclusivesense. As used herein, the term “or” should always be construed in theinclusive sense unless the exclusive sense is specifically indicated orlogically necessary. The exclusive sense of “or” is specificallyindicated when, for example, the term “or” is paired with the term“either”, as in “either A or B.” As another example, the exclusive sensemay also be specifically indicated by appending “exclusive” or “but notboth” after the list of items, as in “A or B, exclusive” and “A or B butnot both.” Moreover, the description of resources, operations, orstructures in the singular shall not be read to exclude the plural.Conditional language, such as, among others, “can,” “could,” “might,” or“may,” unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or steps.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. Adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known,” and terms of similar meaning should not beconstrued as limiting the item described to a given time period or to anitem available as of a given time, but instead should be read toencompass conventional, traditional, normal, or standard technologiesthat may be available or known now or at any time in the future. Thepresence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent.

What is claimed is:
 1. A printed circuit board, comprising: a pluralityof electrical traces for distributing power within a power system; and adistributed hotspot detection grid comprising a plurality of passivetemperature sensors and a detection circuit that is configured tomonitor signals output by the passive temperature sensors; wherein thedistributed hotspot detection grid is configured to send a shut downsignal to one or more power supplies of the power system if thedetection circuit detects a temperature increase; and a kill switchdevice, the kill switch device configured to receive the shut downsignal from the distributed hotspot detection grid and, in response,turn off the one or more power supplies.
 2. The printed circuit board ofclaim 1, wherein the plurality of passive temperature sensors includesone or more of: negative temperature coefficient (NTC) thermistors;resistance temperature detectors (RTDs); positive temperaturecoefficient (PTD) thermistors; thermocouples.
 3. The printed circuitboard of claim 2, wherein an output of the distributed hotspot detectiongrid is configured such that a baseline signal of the output of thedistributed hotspot detection grid is equal to a signal necessary forthe one or more power supplies to operate.
 4. The printed circuit boardof claim 3, wherein the output of the distributed hotspot detection gridis tied into one or more electrical traces containing one or moresignals necessary for the one or more power supplies to operate.
 5. Theprinted circuit board of claim 1, wherein the plurality of electricaltraces are connected to the one or more power supplies of the powersystem through an interface.
 6. The printed circuit board of claim 1,wherein the plurality of passive temperature sensors comprises aplurality of negative temperature coefficient (NTC) thermistors.
 7. Theprinted circuit board of claim 6, wherein the detection circuitcomprises a plurality of comparator circuits.
 8. The printed circuitboard of claim 7, wherein there is a 1-to-1 correspondence between theplurality of comparator circuits and the plurality of NTC thermistors,such that each NTC thermistor is connected to a respective comparatorcircuit of the detection circuit.
 9. The printed circuit board of claim7, wherein a subset of NTC thermistors of the plurality of NTCthermistors is connected to a different comparator circuit of theplurality of comparator circuits, the subset comprises one or more NTCthermistors.
 10. The printed circuit board of claim 1, wherein the oneor more power supplies include a latching device configured to latcheach of the respective power supply in a power off state after receiptof the shut down signal from the distributed hotspot detection grid. 11.The printed circuit board of claim 1, wherein the detection circuit isdisplaced on a distal end of the printed circuit board opposite aninterface for one or more power supplies.
 12. The printed circuit boardof claim 1, wherein the detection circuit includes a plurality of outputsignals, each output signal configured to send the shut down signal toone of the one or more power supplies of the power system.
 13. A method,comprising: distributing a plurality of passive temperature sensors anda detection circuit on a printed circuit board, the detection circuitconnected to an output of each of the plurality of passive temperaturesensors; sensing, by at least one passive temperature sensor of theplurality of passive temperature sensors, an increase in temperature onthe printed circuit board; receiving, by a detection circuit, a voltagelevel on an output of the at least one passive temperature sensor;detecting, by the detection circuit, the increase in temperature on theprinted circuit board; and sending, by the detection circuit, a shutdown signal to a kill switch device on the printed circuit board, thekill switch device configured to turn off the one or more power supplieswhen triggered.
 14. The method of claim 13, wherein the at least onepassive temperature sensor distributed on a printed circuit board is oneof: a negative temperature coefficient (NTC) thermistor; a resistancetemperature detector (RTD); a positive temperature coefficient (PTD)thermistor; a thermocouple.
 15. The method of claim 13, whereindetecting the increase in temperature comprises comparing, by at leastone comparator circuit of the detection circuit, the voltage level fromthe at least one passive temperature sensor to a threshold value. 16.The method of claim 13, wherein the plurality of passive temperaturesensors comprises a plurality of negative temperature coefficient (NTC)thermistors, and wherein the detection circuit comprises a plurality ofcomparator circuits.
 17. A method, comprising: distributing a pluralityof passive temperature sensors and a detection circuit on a printedcircuit board, the detection circuit connected to an output of each ofthe plurality of passive temperature sensors; sensing, by at least onepassive temperature sensor of the plurality of passive temperaturesensors, an increase in temperature on the printed circuit board;receiving, by a detection circuit, a voltage level on an output of theat least one passive temperature sensor; detecting, by the detectioncircuit, the increase in temperature on the printed circuit board; andsending, by the detection circuit, a shut down signal comprising sendingthe shut down signal to a kill switch device in each of the one or morepower supplies, the kill switch device configured to turn off therespective one of the one or more power supplies.
 18. The method ofclaim 17, wherein the at least one passive temperature sensordistributed on a printed circuit board is one of: a negative temperaturecoefficient (NTC) thermistor; a resistance temperature detector (RTD); apositive temperature coefficient (PTD) thermistor; a thermocouple. 19.The method of claim 17, wherein the plurality of passive temperaturesensors comprises a plurality of negative temperature coefficient (NTC)thermistors, and wherein the detection circuit comprises a plurality ofcomparator circuits.
 20. The method of claim 17, wherein detecting theincrease in temperature comprises comparing, by at least one comparatorcircuit of the detection circuit, the voltage level from the at leastone passive temperature sensor to a threshold value.